NIP - The cut made by waves in a shoreline of emergence. 



NODAL ZONE - An area in which the predominant direction of the LONGSHORE 

 TRANSPORT changes. 



NODE - That part of a STANDING WAVE where the vertical motion is least 

 and the horizontal velocities are greatest. Nodes are associated 

 with CLAPOTIS and with SEICHE action resulting from wave reflections. 

 See also LOOP. 



NOURISHMENT - The process of replenishing a beach. It may be brought 

 about naturally, by longshore transport, or artificially by the 

 deposition of dredged materials. 



OCEANOGRAPHY - The study of the sea, embracing and indicating all 



knowledge pertaining to the sea's physical boundaries, the chem- 

 istry and physics of sea water, and marine biology. 



OFFSHORE - (1) In beach terminology, the comparatively flat zone of 



variable width, extending from the breaker zone to the seaward edge 

 of the Continental Shelf. (2) A direction seaward from the shore. 

 (See Figure A-1.) 



OFFSHORE BARRIER - See BARRIER BEACH. 



OFFSHORE CURRENT - (1) Any current in the offshore zone. (2) Any 

 current flowing away from shore. 



OFFSHORE WIND - A wind blowing seaward from the land in the coastal area. 



ONSHORE - A direction landward from the sea. 



ONSHORE WIND - A wind blowing landward from the sea in the coastal area. 



OPPOSING WIND - In wave forecasting, a wind blowing in a direction opposite 

 to the ocean-wave advance; generally, same as headwind. 



ORBIT - In water waves, the path of a water particle affected by the wave 

 motion. In deepwater waves the orbit is nearly circular and in 

 shallow-water waves the orbit is nearly elliptical. In general, 

 the orbits are slightly open in the direction of wave motion giving 

 rise to MASS TRANSPORT. (See Figure A- 3.) 



ORBITAL CURRENT - The flow of water accompanying the orbital movement of 



the water particles in a wave. Not to be confused with wave-generated 

 LITTORAL CURRENTS. (See Figure A- 3.) 



ORTHOGONAL - On a wave- refraction diagram, a line drawn perpendicularly to 

 the wave crests. (See Figure A-6.) 



OSCILLATION - A periodic motion backward and forward. To vibrate or vary 

 above and below a mean value. 



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